Page:Popular Science Monthly Volume 37.djvu/528

512 this is chrysolæma. In the interior of California the shore larks are still smaller and redder (variety rubea), while northward and coastwise appears a small lark with more streaked plumage; this is strigata. All these can be generally recognized by an expert ornithologist, and doubtless a closer analysis would reveal the basis for still finer subdivisions.

In 1871 Dr. Joel A. Allen published his masterly paper on the Mammals and Winter Birds of Florida. This memoir has had the practical effect of making all our ornithologists, for the most part against their will, believers in the theory of derivation of species.

Dr. Allen took up, as a matter of serious study, the variations in individual birds. He showed that the variation of individuals of the same species was far greater than had been supposed, and that the characters relied on to distinguish species were often due to slight increase in these variations. For example, in Northern birds the bodies would be larger, the bills smaller than in birds of the same species from the South, and the coloration of birds was often directly related to the degree of rainfall. He showed, in brief, that each one of these many variations must be held to define a distinct species, or else that the number of species of American birds would have to be greatly reduced, and the range of variation inside the species would need to be correspondingly extended.

This claim for attention on the part of the despised variety produced much consternation among students of birds. But facts must be recognized; and the final result has been, that we have now extended our idea of each species until it is large enough to include all that we know of intermediate and varying forms. When a hiatus appears, whether existing either in fact or in our material for study, there we put our line of definition. "We can only predicate and define species at all," says Dr. Coues, "from the mere circumstance of missing links. Species are the twigs of a tree separated from the parent stem. We name and arrange them arbitrarily, in default of a means of reconstructing the whole tree in accordance with Nature's ramifications."